Air Quality Lichen Sensitivity Ratings

Air quality sensitivity ratings are based on our own field studies (95 species) and a world-wide literature review emphasizing references from western North America (110 species, of which 46 were not rated in our own studies). Lichen sensitivy can vary with climate, the composition and proportion of airborne pollutants in the air, and topographic exposure. The ratings presented here are specific to the Northwest USA and may or may not be accurate for other regions.

 

95 ratings were calculated from our field studies of lichen communities in Oregon and Washington, including the urban areas of Portland, Salem, Corvallis, Albany, Eugene, Vancouver, Tacoma, and Olympia, and other public lands in the Willamette Valley, the Washington State Interstate Highway-5 corridor, the Gifford-Pinchot, Siuslaw, Willamette, and Mt. Hood National Forests and the Columbia River Gorge National Scenic Area. Lichens with a rating of 10 are most sensitive to the regional mixture of pollutants occuring in the Pacific Northwest west of the Cascade Range crest; lichens with a rating of 1 are most tolerant. These are our most current, regionally-based estimates.

 

Because few sensitivity studies have been conducted in the Pacific Northwest and lichen sensitivity can vary with climate, regional pollution mixes, and topographic exposure, we have used a general rating system (sensitive, intermediate or tolerant) to apply sensitivities reported in the literature. Literature reports used to estimate general sensitivities have been tabulated by species to create a guide to the Pacific Northwest lichens and their sensitivities to air pollution, complete with photographs and additional notes. Below are estimated sulfur dioxide tolerances for general ratings used in the guide.

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